Low-Capacitance Contact For Long Gate-Length Devices with Small Contacted Pitch

ABSTRACT

Disclosed are planar and non-planar field effect transistor (FET) structures and methods of forming the structures. The structures comprise segmented active devices (e.g., multiple semiconductor fins for a non-planar transistor or multiple semiconductor layer sections for a planar transistor) connected at opposite ends to source/drain bridges. A gate electrode is patterned on the segmented active devices between the source/drain bridges such that it has a reduced length between the segments (i.e., between the semiconductor fins or sections). Source/drain contacts land on the source/drain bridges such that they are opposite only those portions of the gate electrode with the reduced gate length. These FET structures can be configured to simultaneously maximize the density of the transistor, minimize leakage power and maintain the parasitic capacitance between the source/drain contacts and the gate conductor below a preset level, depending upon the performance and density requirements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/767,635filed Jun. 25, 2007, the complete disclosure of which, in its entirety,is herein incorporated by reference.

BACKGROUND

1. Field of the Invention

The embodiments of the invention generally relate to field effecttransistors, and, more particularly, to a low-capacitance contact forlong gate-length planar and non-planar devices with small contactedpitch.

2. Description of the Related Art

Despite current lithography techniques which allow devices to be formedwith reduced dimensions, the scaling of complementary metal oxidesemiconductor (CMOS) devices and particularly, the scaling of CMOStransistor gate lengths is limited by leakage power. Logic circuitdensity is limited by the contacted pitch of field effect transistors(i.e., the minimum metal line width spacing plus addition for via orcontact covers or landing pads) and this contacted pitch is in turnlimited by the (non-shrinking) gate lengths of the transistors. It wouldbe advantageous over the prior art to provide a transistor structurethat can simultaneously minimize leakage power, minimize parasiticcapacitance between the source/drain contacts and the gate electrode andoptimize device density.

SUMMARY

In view of the foregoing, embodiments of the invention provide planarand non-planar field effect transistor (FET) structures and methods offorming the structures. The structures comprise segmented active devices(e.g., multiple semiconductor fins for a non-planar transistor ormultiple semiconductor layer sections for a planar transistor) connectedat opposite ends to source/drain bridges. A gate electrode is patternedon the segmented active devices between the source/drain bridges suchthat it has a reduced length between the segments (i.e., between thesemiconductor fins or sections). Source/drain contacts land on thesource/drain bridges such that they are opposite only those portions ofthe gate electrode with the reduced gate length. These FET structurescan be configured to simultaneously maximize the density of thetransistor, minimize leakage power and maintain the parasiticcapacitance between the source/drain contacts and the gate conductorbelow a preset level, depending upon the performance and densityrequirements.

More particularly, one embodiment of the FET of the invention comprisesa planar FET. This planar FET can comprise a semiconductor layer with aplurality of first sections and a plurality of second sections. Thesecond sections can traverse and contact the first sections.Specifically, the first sections can be positioned parallel to eachother, the second sections can be positioned parallel to each other andthe first sections can be positioned perpendicular to the secondsections such that spaces are formed between the sections. These spacescan be insulator-filled, the first sections can comprise the channelregions of the transistor and the second sections can comprisesource/drain diffusion regions.

A gate conductor can be positioned between the second sections and canextend across the first sections and the spaces (e.g., parallel to thesecond sections). The gate conductor can be patterned such that itcomprises first portions above the first sections and second portionsabove the spaces. The first portions can have a first length that isgreater than a second length of the second portions. For example, thelength of the first portions can range from approximately 1.2 to 2.5times longer than the length of the second portions. A gate dielectriclayer can be positioned between the first sections and the gateconductor.

A plurality of source/drain contacts can connect to the second sections.The contacts can be positioned above the second sections between thefirst sections such that they are opposite the second (shorter) portionsof the gate conductor. The different lengths of the gate conductor and apitch between the contacts can be predetermined based on performance anddensity requirements for the transistor so as to simultaneously maximizethe density the transistor, minimize leakage power and maintainparasitic capacitance below a preset level.

Other embodiments of the FET of the invention comprise non-planar FETs,such as finFETs or trigate FETs. Each of these non-planar FETs cancomprise a plurality of semiconductor fins and a plurality ofsemiconductor mesas on the substrate. The semiconductor mesas cantraverse and contact the semiconductor fins. Specifically, thesemiconductor fins can be positioned parallel to each other, thesemiconductor mesas can be positioned parallel to each other and thesemiconductor fins can be positioned perpendicular to the semiconductormesas such that a plurality of spaces are between the semiconductorfins. The semiconductor fins can have a height to width ratio ofapproximately 2:3 to 3:2 so that the non-planar FET is configured as atrigate FET. Alternatively, the semiconductor fins can have a height towidth ratio of greater than approximately of 4:1 so that the non-planarFET is configured as a fin-type or double-gate FET. Additionally, thesemiconductor fins can comprise the channel regions of the transistorand the semiconductor mesas can comprise source/drain diffusion regions.

A gate conductor can be positioned between the semiconductor mesas andcan extend across the semiconductor fins and the spaces (e.g., parallelto the semiconductor mesas). The gate conductor can be patterned suchthat it comprises first portions over the semiconductor fins (i.e.,above the channel regions) and second portions over the spaces. Thefirst portions can have a first length that is greater than the secondlength of the second portions. For example, the length of the firstportions (i.e., the first length) can range from approximately 1.2 to2.5 times longer than the length of the second portions (i.e., thesecond length).

A gate dielectric layer can be positioned between the semiconductor finsand the gate conductor (i.e., on the opposing sidewalls and top surfaceof the fin-shaped semiconductor fins below the gate conductor). Thisgate dielectric layer can comprise a first region on the top surface anda second region on the opposing sidewalls. The first region can have thesame thickness and can comprise the same dielectric material as thesecond region. Alternatively, the first region can have a differentthickness and/or can comprise a different dielectric material than thesecond region.

A plurality of source/drain contacts can connect to the semiconductormesas. The contacts can be positioned above the semiconductor mesasbetween the semiconductor fins such that they are opposite the second(shorter) portions of the gate conductor. As with the previouslydescribed planar embodiment, the different lengths of the gate conductorand a pitch between the contacts are predetermined based on performanceand density requirements for the transistor in order to simultaneouslymaximize the density of transistor, minimize leakage power and maintainparasitic capacitance below a preset level.

One embodiment of the method of the invention comprises forming a planarFET, as described above. Specifically, a semiconductor layer with aplurality of second sections that traverse and contact a plurality offirst sections is formed on a substrate. The semiconductor layer isformed such that the first sections and the second sections areseparated by spaces that are filled with an insulator. For example, thesemiconductor layer can be patterned with the first sections parallel toeach other, the second sections parallel to each other and the firstsections perpendicular to the second sections such that spaces areformed between the sections.

A gate dielectric layer can be formed on the first sections and a gateconductor can be formed on the gate dielectric layer. Specifically, thegate conductor can be patterned on the semiconductor layer between thesecond sections (e.g., parallel to the second sections) such that itextends across the first sections and the spaces. The gate conductor canfurther be patterned with first portions above the first sections andsecond portions above the spaces. More particularly, the first portionscan be patterned with a first length that is greater than a secondlength of the second portions. For example, the gate conductor can beformed such that the first length is approximately 1.2 to 2.5 timeslonger than the second length.

A plurality of source/drain contacts can also be formed to the secondsections. Specifically, these contacts can be formed above the secondsections between the first sections such that they are opposite thesecond (shorter) portions of the gate conductor.

In order to simultaneously maximize the density of the resultingtransistor, minimize leakage power and maintain parasitic capacitancebelow a preset level, the different lengths of the gate conductor and apitch between the contacts can be predetermined (e.g., during the designphase before forming the semiconductor layer) based on performance anddensity requirements.

Another embodiment of the method of the invention comprises forming thenon-planar FETs, as described above. Specifically, a plurality ofsemiconductor fins and a plurality of semiconductor mesas (i.e.,semiconductor regions can be formed on an insulator layer. In order toconfigure the transistor as a trigate FET, these semiconductor bodiescan be formed with a height to width ratio of approximately 2:3 to 3:2.Alternatively, in order to form the transistor as a fin-FET, thesesemiconductor bodies can be formed with a height to width ratio that isgreater than approximately 4:1. Additionally, these semiconductor bodiesare formed such that the semiconductor mesas traverse and contact thesemiconductor fins and such that the semiconductor fins and thesemiconductor mesas are separated by spaces. For example, thesemiconductor bodies can be lithographically patterned with firstsections parallel to each other, with second sections parallel to eachother and with the first sections perpendicular to the second sectionssuch that spaces are formed between the sections

A gate dielectric layer can be formed on the semiconductor fins and agate conductor can formed on the gate dielectric layer. Specifically,the gate dielectric layer can be formed with a first region on the topsurface of the semiconductor fins and a second region on the opposingsidewalls of the semiconductor fins. The first region can be formed withthe same thickness and the same dielectric material as the secondregion. Alternatively, the first region can be formed with at least oneof a different thickness and a different dielectric material than thesecond region.

The gate conductor can be patterned over the gate dielectric material onthe semiconductor fins between the semiconductor mesas (e.g., parallelto the mesa sections) such that it extends across the semiconductor finsand the spaces. The gate conductor can further be patterned with firstportions above the semiconductor fins and second portions above thespaces. More particularly, the first portions can be patterned with afirst length that is greater than a second length of the secondportions. For example, the gate conductor can be formed such that thefirst length is approximately 1.2 to 2.5 times longer than the secondlength.

A plurality of contacts can be formed to the semiconductor mesas.Specifically, these contacts can be formed above the semiconductor mesasbetween the semiconductor fins such that they are opposite the second(shorter) portions of the gate conductor.

In order to simultaneously maximize the density of the resultingtransistor, minimize leakage power and maintain parasitic capacitancebelow a preset level, the different lengths of the gate conductor and apitch between the contacts can be predetermined (e.g., during the designphase before forming of the semiconductor bodies) based on performanceand density requirements for the transistor.

These and other aspects of the embodiments of the invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingembodiments of the invention and numerous specific details thereof, aregiven by way of illustration and not of limitation. Many changes andmodifications may be made within the scope of the embodiments of theinvention without departing from the spirit thereof, and the embodimentsof the invention include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention will be better understood from thefollowing detailed description with reference to the drawings, in which:

FIG. 1 is schematic diagram illustrating a top view of a field effecttransistor;

FIG. 2 is a schematic diagram illustrating a top view of an embodimentof the field effect transistor of the invention;

FIG. 3 is a schematic diagram illustrating a cross-section view of thetransistor of FIG. 2;

FIG. 4 is a schematic diagram illustrating another cross-section view ofthe transistor of FIG. 2;

FIG. 5 is a schematic diagram illustrating a top view of anotherembodiment of the field effect transistor of the invention;

FIG. 6 is a schematic diagram illustrating a cross-section view of thetransistor of FIG. 5;

FIG. 7 is a schematic diagram illustrating another cross-section view ofthe transistor of FIG. 5;

FIGS. 8 and 9 are exploded views of alternate configurations for aportion of FIG. 7;

FIG. 10 is a schematic diagram illustrating another cross-section viewof the transistor of FIG. 5;

FIG. 11 is a flow diagram illustrating an embodiment of the method ofthe invention; and

FIG. 12 is a flow diagram illustrating another embodiment of the methodof the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiments of the invention and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting embodiments that are illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale. Descriptions of well-known components and processingtechniques are omitted so as to not unnecessarily obscure theembodiments of the invention. The examples used herein are intendedmerely to facilitate an understanding of ways in which the embodimentsof the invention may be practiced and to further enable those of skillin the art to practice the embodiments of the invention. Accordingly,the examples should not be construed as limiting the scope of theembodiments of the invention.

FIG. 1 illustrates semiconductor structure 100 comprising multipleplanar field effect transistors 101 a-c. More specifically, thestructure 100 comprises multiple gate conductors 130 that extend acrossa semiconductor layer 110. Shared source/drain contacts are disposedbetween the gate conductors 130 and contact the semiconductor layer 110.

As mentioned above, logic circuit density (e.g., the density of thestructure 100) is limited by the contacted pitch 140 of field effecttransistors 101 a-c. This contacted pitch 140 is in turn limited by the(non-shrinking) gate lengths 150 of the transistors 101 a-c.Specifically, the contacted pitch 140 is the spacing betweencorresponding points on contacts 120 located on opposite sides of thegate conductor 130. The contacted pitch 140, therefore, includes boththe gate length 150 and the distances 160 between the gate conductor 130the source/drain contacts 120. However, scaling of the gate length 150is limited due to resulting leakage power and scaling of the distance160 between the gate conductor and the source/drain contacts is limiteddue to parasitic capacitance which degrades performance and increasesthe closer the source/drain contacts 120 are to the gate conductor 130.Therefore, it would be advantageous over the prior art to provide atransistor structure that can be use to minimize parasitic capacitancebetween the source/drain contacts and the gate electrode, minimizeleakage power and maximize device density.

In view of the foregoing, embodiments of the invention provide planarand non-planar field effect transistor (FET) structures and methods offorming the structures. The structures are made up of segmented activedevices (e.g., multiple semiconductor fins for a non-planar transistoror multiple semiconductor layer sections for a planar transistor)connected at opposite ends to source/drain bridges. A gate electrode ispatterned on the segmented active devices between the source/drainbridges such that it has a reduced length between the segments (i.e.,between the semiconductor fins or sections). Source/drain contacts landon the source/drain bridges such that they are opposite only thoseportions of the gate electrode with the reduced gate length. These FETstructures can be configured to simultaneously maximize the density ofthe transistor, minimize leakage power and maintain the parasiticcapacitance between the source/drain contacts and the gate conductorbelow a preset level, depending upon the performance and densityrequirements.

FIGS. 2-4 illustrate a top view and various cross-section views (e.g.,cross-section A-A′ and B-B′), respectively, of one embodiment of the FETof the invention. Specifically, referring to FIG. 2, the semiconductorstructure 200 comprises a plurality of planar FETs 201 a-c. Each planarFET 201 a-c can comprise a semiconductor layer 210 with a plurality offirst sections 211 and at least two second sections 212. The secondsections 212 can traverse and contact the first sections 211.Specifically, the first sections 211 can be positioned parallel to eachother, the second sections 212 can be positioned parallel to each otherand the first sections 211 can be positioned perpendicular to the secondsections 212 such that spaces 270 (e.g., rectangular-shaped spaces) areformed between the sections 211, 212, as illustrated in FIG. 2. Thespaces 270 can be filled by an insulator (e.g., SiO₂).

For each transistor 201, a gate conductor 230 can be positioned betweentwo second sections 212 and can extend across the first sections 211 andthe spaces 270 (e.g., parallel to the two second sections 212) (see alsothe cross-sections of FIGS. 3 and 4). The gate conductor 230 can bepatterned such that it comprises first portions 231 above the firstsections 211 and second portions 232 above the spaces 270 between thefirst and seconds sections. The first portions 231 can have a firstlength 251 that is greater than a second length 252 of the secondportions 231. For example, the length 251 of the first portions 231 canrange from approximately 1.2 to 2.5 times longer than the length 252 ofthe second portions 232. A gate dielectric layer 280 (see FIG. 4) can bepositioned between the first sections 211 and the gate conductor 230(i.e., on the top surface of the first sections 211).

Thus, the portions of the first sections 211 below the gate conductor230 form the channel regions of the transistor 201 and the secondsections 212 form source/drain diffusion regions (i.e., source/drainbridges). The second sections 212 can further be used as sharedsource/drain diffusion regions for multiple transistors 201 a-c.Additionally, it is anticipated that while the structure 200, asillustrated in FIGS. 2-4, comprises multiple planar transistors 201 a-c,a gate conductor bridge can be incorporated into the structure 200 suchthat it extends across and connects each of the multiple gate conductors230 in order to form a single planar FET, according to the invention.

A plurality of source/drain contacts 220 can connect to the secondsections 212 (i.e., to the source/drain bridges) on each side of thegate conductor 230 (see also the cross-section of FIG. 3). The contacts220 can be positioned above the second sections 212 between the firstsections 211 such that they are opposite the second (shorter) portions232 and not adjacent to the first (longer) portions 231 of the gateconductor 230.

Consequently, during the design of the planar transistor 201 of theinvention a trade-off can be made between minimizing parasiticcapacitance and leakage power and optimizing device density.Specifically, forming the gate conductor 230 with longer and shorterportions 231, 232, as described above, allows a designer to reduceparasitic capacitance without decreasing the gate length 251 over theactive silicon regions of the first sections 211 (causing an increase inleakage power) and without further increasing the contacted pitch 240.Alternatively, forming the gate conductor 230, as described above,allows the device density to be increased by decreasing the distance 260between the contacts and the shorter portions 232 of the gate conductor230 without reducing the gate length 251 over the active silicon regions(causing an increase in leakage power) and without significantlyincreasing parasitic capacitance. Therefore, the different lengths251-252 of the gate conductor 230 and a pitch 240 between the contacts320 (i.e., a contacted pitch) can be predetermined so as tosimultaneously maximize the density of the transistor, minimize leakagepower, and maintain any parasitic capacitance (e.g., between thecontacts and the gate conductor) below a preset level, as dictated bydensity and performance requirements.

FIGS. 5-10 illustrate a top view and various cross-section views (e.g.,cross-section A-A′, B-B′ and C-C′), respectively, of another embodimentof the FET of the invention. Specifically, referring to FIG. 5, thesemiconductor structure 300 comprises a plurality of multi-gatednon-planar FETs 301 a-c, such as finFETs or trigate FETs. Suchmulti-gated non-planar field effect transistors (FETs) were developed toprovide scaled devices with faster drive currents and reduced shortchannel effects over planar FETs. FinFETs are non-planar transistors inwhich the channel region is formed at the center of a thin semiconductorfin with the source/drain regions at opposing ends. Due to the height towidth ratio of the finFET fin, the gates are effective only on theopposing sidewalls of the fin and not the top surface. Trigate FETs havea similar structure to that of finFETs; however, the fin height to widthratio is such that the gates are effective on three sides of the channelregion, including the top surface and the opposing sidewalls.

Thus, each of these non-planar FETs 301 a-c can comprise a plurality offin-shaped semiconductor bodies (fins) 311 and at least twosemiconductor mesas 312 (e.g., source/drain bridges) on a substrate 391.The semiconductor mesas 312 can traverse and contact the semiconductorfins 311. Specifically, the semiconductor fins 311 can be positionedparallel to each other, the semiconductor mesas 312 can be positionedparallel to each other and the semiconductor fins 311 can be positionedperpendicular to the semiconductor mesas 312. A plurality of spaces 370(e.g., rectangular-shaped spaces) separate the semiconductor bodies 311,312 (see also the cross-sections of FIGS. 6 and 7). For trigate FETs,the semiconductor fins 311 can have a height 313 to width 314 ratio ofapproximately 2:3 to 3:2. Alternatively, for fin-FETs, the semiconductorfins 311 can have a height 313 to width 314 ratio of greater thanapproximately of 4:1.

For each transistor 301 a-c, a gate conductor 330 can be positionedbetween two semiconductor mesas 312 and can extend across thesemiconductor fins 311 and the spaces 370 (e.g., parallel to thesemiconductor mesas 312) (see the cross-sections of FIGS. 6 and 7). Thegate conductor 330 can be patterned such that it comprises firstportions 331 over the semiconductor fins 311 (i.e., adjacent to the topsurface and opposing sidewalls of the fins) and second portions 332 overthe spaces 370. The first portions 331 can have a first length 351 thatis greater than the second length 352 of the second portions 332. Forexample, the length 351 of the first portions 331 can range fromapproximately 1.2 to 2.5 times longer than the length 352 of the secondportions 332. Those skilled in the art will recognize that, unlike inthe planar embodiment described above, gate critical dimension down thesemiconductor fin 331 is in the vertical direction so roundingassociated with this PC pattern is not problematic.

A gate dielectric layer 380 can be positioned between the semiconductorfins 311 and the gate conductor 330 (i.e., on the top surface andopposing sidewalls) (see FIG. 7). This gate dielectric layer 380 cancomprise a first region 381 on the top surface and a second region 382on the opposing sidewalls. The first region 381 can have the samethickness and can comprise the same dielectric material as the secondregion 382 (see FIG. 8). Alternatively, the first region 381 can have adifferent thickness and/or can comprise a different dielectric material(e.g., an oxide and a nitride, respectively) than the second region 382(see FIG. 9). The thickness and the dielectric materials can be variedin tri-gate FETs in order to tune drive current.

Thus, the portion of the semiconductor fins 311 below the gate conductor330 forms the channel regions of the transistor and the semiconductormesas 312 form the source/drain diffusion regions (i.e., source/drainbridges) of the transistor. The semiconductor mesas 312 can further beused as shared source/drain diffusion regions for multiple transistors301 a-c. Additionally, it is anticipated that while the structure 300,as illustrated, comprises multiple planar transistors 301 a-c, a gateconductor bridge can be incorporated into the structure 300 such that itextends across and connects each of the multiple gate conductors 330 toform a single non-planar FET, according to the invention.

A plurality of contacts 320 can connect to the semiconductor mesas 312(i.e., to the source/drain bridges). The contacts 320 can be positionedabove the semiconductor mesas 312 between the semiconductor fins 311such that they are opposite the second (shorter) portions 332 (see thecross-section of FIG. 6) and not adjacent to the first (longer) portions331 of the gate conductor 330 (see the cross-section of FIG. 10).

Consequently, during the design of the non-planar transistor of theinvention a trade-off can be made between minimizing parasiticcapacitance and leakage power and maximizing device density.Specifically, forming the gate conductor 330 with longer and shorterportions 331, 332, as described above, allows a designer to reduceparasitic capacitance without decreasing the gate length 351 over theactive silicon regions of the semiconductor fins 311 (causing anincrease in leakage power) and without further increasing the contactedpitch 340. Alternatively, forming the gate conductor 330, as describedabove, allows the device density to be increased by decreasing thedistance 360 between the contacts and the shorter portions 332 of thegate conductor 330 without reducing the gate length 351 over the activesilicon regions (causing an increase in leakage power) and withoutsignificantly increasing parasitic capacitance. Therefore, the length352 of the gate conductor 330 over the spaces 370, the distance 360between the contacts 320 and the gate conductor 330 and a pitch 340between the contacts 320 (i.e., a contacted pitch) can be predeterminedso as to simultaneously maximize the density of the transistor, minimizeleakage power and maintain any parasitic capacitance (e.g., between thecontacts and the gate conductor) below a preset level as dictated bydevice density and performance requirements.

Referring to FIG. 11 in combination with FIG. 2, one embodiment of themethod comprises forming a planar FET 201. The transistor 201 isdesigned to simultaneously maximize transistor density, minimize leakagepower and maintain the parasitic capacitance (e.g., between source/draincontacts 220 and the gate conductor 230) below a preset level (1102), asdictated by performance and density requirements. This is accomplishedby predetermining different lengths 251, 252 of the gate conductor 230over different sections of the FET (1103) and predetermining the pitch240 between the contacts 220 (1104), as described in greater detailbelow. Then, the transistor 201 is formed using conventional planar FETprocessing techniques. Specifically, a semiconductor layer 210 with aplurality of second sections 212 (at least two second sections) thattraverse and contact a plurality of first sections 211 is formed on adielectric substrate 291 (e.g., a buried oxide layer of asilicon-on-insulator (SOI) wafer or bulk silicon wafer) (1106). Thesemiconductor layer 210 is formed such that the first sections 211 andthe second sections 212 are separated by insulator-filled spaces 270.For example, a semiconductor layer 210 of a silicon-on-insulator (SOI)or bulk silicon wafer can be lithographically patterned with the firstsections 211 parallel to each other, with the second sections 212parallel to each other and with the first sections 211 perpendicular tothe second sections 212, such that spaces 270 (e.g., rectangular-shapedspaces) are formed between the sections 211, 212 (1106). These spaces270 can be filled with an insulator 293, such as SiO₂, for example, bydepositing and planarizing the insulator (1108)

A gate dielectric layer 280 can be formed (e.g., grown or deposited) onthe first sections 211 (1110) and a gate conductor 230 can be formed onthe gate dielectric layer 280 (1112). Specifically, a gate conductor 230can be lithographically patterned onto the semiconductor layer 210 suchthat it is positioned between the two second sections 212 (e.g.,parallel to the second sections 212) and such that it extends across thefirst sections 211 and the spaces 270 (1113-1114) (see also thecross-sections of FIGS. 3 and 4). The gate conductor 230 can further bepatterned with first portions 231 above the first sections 211 andsecond portions 232 above the spaces 270 (1115). More particularly, thefirst portions 231 can be patterned with a first length 251 that isgreater than a second length 252 of the second portions 232 (1116). Forexample, the gate conductor 230 can be patterned such that the firstlength 251 is approximately 1.2 to 2.5 times longer than the secondlength 252.

Additional processing can be performed in conjunction with theabove-described processes, in order to complete the planar FET of thisembodiment (1117). This additional processing may include, but is notlimited to: doping the source/drain bridges (i.e., the second sections212); doping the source/drain extensions (i.e., the areas of firstsections 211 between the gate conductor 230 and the second sections212); forming halos; forming spacers on the gate sidewalls; formingsilicides (e.g., Co, Ni, Etc.) on the top surface of the first sections211, the second sections 212, and/or the gate conductor 230 (if the gateconductor is formed with a polysilicon material and without a cap);depositing and planarizing an additional dielectric layer 292; forminggate contacts; and forming the source/drain contacts 220 (i.e., thecontacts 220 to the second sections 212, as described above).

Specifically, a plurality of source/drain contacts 220 can be formed tothe second sections 211 (1118) (see also the cross section of FIG. 3).These contacts 220 can be formed above the second sections 212 (1119)between the first sections 211 (1120) such that they are opposite thesecond (shorter) portions 232 (see the cross-section of FIG. 3) andparticularly not adjacent to the second (longer) portions 231 of thegate conductor 230 (1121) (see the cross-section of FIG. 4).

As mentioned above (at process 1102), the different lengths 251-252 ofthe gate conductor 230 and a pitch 240 between the contacts 220 (i.e., acontacted pitch) can be predetermined based on a trade-off betweenperformance and density requirements for the transistor 201 so as tosimultaneously maximize the density of the transistor, minimize leakagepower and maintain any parasitic capacitance (e.g., between the contactsand the gate conductor) below a preset level. For example, the lengths251 and 252 of the gate conductor 230 and the pitch 240 can bepredetermined during the design phase (1102) to reduce parasiticcapacitance without reducing the gate length 251 of over the activesilicon regions (causing an increase in leakage power) and withoutfurther increasing the contacted pitch 240. Alternatively, the lengths251 and 252 of the gate conductor 230 and the pitch 240 can bepredetermined to allow the device density to be increased withoutreducing the gate length 251 over the active silicon regions (causing anincrease in leakage power) and without significantly altering theparasitic capacitance.

Referring to FIG. 12 in combination with FIG. 5, another embodiment ofthe method comprises forming the non-planar FET 301. The transistor 301is designed to simultaneously maximize the density of the transistor,minimize leakage power and maintain the parasitic capacitance (e.g.,between source/drain contacts 320 and the gate conductor 330) below apreset level, as dictated by performance and density requirements(1202). This is accomplished by predetermining the different lengths351, 352 of the gate conductor 330 over different sections of the FET(1203) and predetermining the pitch 340 between the contacts 320 (1104),as described in greater detail below. Then, the transistor 301 is formedusing conventional processing techniques for non-planar FETs.Specifically, a plurality of first (fin-shaped) semiconductor bodies 311(i.e., first fins) and a plurality of semiconductor mesas 312 (i.e.,second fins) can be lithographically patterned into a silicon layer of asilicon-on-insulator (SOI) or bulk silicon wafer to a buried insulator(e.g., a buried oxide layer) 391 (1206).

As mentioned above, finFETs are non-planar transistors in which thechannel region is formed at the center of a thin semiconductor fin withthe source/drain regions at opposing ends. Due to the height to widthratio of the finFET fin, the gates are effective only on the opposingsidewalls of the fin and not the top surface. Trigate FETs have asimilar structure to that of finFETs; however, the fin height to widthratio is such that the gates are effective on three sides of the channelregion, including the top surface and the opposing sidewalls. Thus, inorder to form a trigate FET, the semiconductor fins 311 are patternedand etched such that they are formed with a height 313 to width 314ratio of approximately 2:3 to 3:2 (1207). Alternatively, in order toform a fin-FET, the semiconductor fins 311 are patterned and etched suchthat they are formed with a height 313 to width 314 ratio that isgreater than approximately 4:1 (1208).

Additionally, the first and semiconductor mesas 311-312 are formed suchthat the semiconductor mesas 312 traverse and contact the semiconductorfins 311 and such that the semiconductor fins 311 and the semiconductormesas 312 are separated by spaces 370. For example, the semiconductorbodies can be patterned with semiconductor fins 311 parallel to eachother, with semiconductor mesas 312 parallel to each other and with thesemiconductor fins 311 perpendicular to the semiconductor mesas 312 suchthat spaces 370 (e.g., rectangular-shaped spaces) are formed between thesemiconductor bodies 311-312.

A gate dielectric layer 380 can be formed (e.g., grown or deposited) onthe semiconductor fins 311 (1210) (see FIG. 7) and a gate conductor 330can formed on the gate dielectric layer 380 (1214). Specifically, thegate dielectric layer 380 can be formed with a first region 381 on thetop surface of the semiconductor fins 311 and a second region 382 on theopposing sidewalls of the semiconductor fins 311. The first region 381can be formed with the same thickness and the same dielectric materialas the second region 382 (1211, see FIG. 8). Alternatively, usingvarious known techniques, the first region 381 can be formed with adifferent thickness and/or a different dielectric material (e.g.,nitride, oxide, etc.) than the second region 382 (1212, see FIG. 9),e.g., to tune the drive current of a trigate FET.

The gate conductor 330 can be lithographically patterned (at process1214) over the gate dielectric material 380 on the semiconductor fins311 between the semiconductor mesas 312 (e.g., parallel to the secondsections) such that it extends across the semiconductor fins 311 (i.e.,on the top surface and opposing sidewalls of the semiconductor fins 311)and the spaces 370 (1215-1216) (see the cross-sections of FIGS. 6 and7). The gate conductor 330 can further be patterned with first portions331 above the semiconductor fins 311 and second portions 332 above thespaces 370 (1217). More particularly, the first portions 331 can bepatterned with a first length 351 that is greater than a second length352 of the second portions 332 (1218). For example, the gate conductor330 can be formed such that the first length 351 is approximately 1.2 to2.5 times longer than the second length 352.

A finFET is a non-planar transistor in which the channel region isformed at the center of a thin semiconductor fin with the source/drainregions at opposing ends. Due to the thinness of the fin, the gates areeffectively formed only on the opposing sidewalls of the semiconductorfin adjacent to the channel region. A trigate FET has a similarstructure to that of finFET; however, the semiconductor fin width andheight are such that gates can effectively be formed on three sides ofthe channel region, including the top surface and the opposing sidewalls

Additional processing can be performed in conjunction with theabove-described processes, in order to complete the non-planar FETs ofthis embodiment (1217). This additional processing may include, but isnot limited to: doping the source/drain bridges (i.e., the semiconductormesas 312); doping the source/drain extensions (i.e., the areas ofsemiconductor fins 311 between the gate conductor 330 and thesource/drain bridges 312); forming halos; forming fin spacers adjacentto the semiconductor fins 311; forming spacers on the gate sidewalls;forming silicides (e.g., Co, Ni, Etc.) on the top surface of thesemiconductor fins 311, the semiconductor mesas 312, and/or the gateconductor 330 (if the gate conductor is formed with a polysiliconmaterial and without a cap); depositing and planarizing an additionaldielectric layer 392; forming gate contacts; and forming thesource/drain contacts 320 (i.e., the contacts 320 to the semiconductormesas 312, as described above).

Specifically, a plurality of source/drain contacts 320 can be formed tothe semiconductor mesas 312 (1220) (see the cross-sections of FIGS. 6and 10). These contacts 320 can be formed above the semiconductor mesas312 (1221) between the semiconductor fins 311 (1222) such that they areopposite the second (shorter) portions 332 (see FIG. 6) and not adjacentto the first (longer) portions 331 of the gate conductor 330 (see FIG.10) (1223).

As mentioned above (at process 1202), the different lengths 351-352 ofthe gate conductor 330 and a pitch 340 between the contacts 320 (i.e., acontacted pitch) can be predetermined based on a trade-off betweenperformance and density requirements for the transistor 301 so as tosimultaneously maximize the density of the transistor, minimize leakagepower and maintain any parasitic capacitance (e.g., between the contactsand the gate conductor) below a preset level. For example, the lengths351 and 352 of the gate conductor 230 and the pitch 340 can bepredetermined during the design phase (1102) to reduce parasiticcapacitance without reducing the gate length 351 of over the activesilicon regions (causing an increase in leakage power) and withoutfurther increasing the contacted pitch 340. Alternatively, the lengths351 and 352 of the gate conductor 330 and the pitch 340 can bepredetermined to allow the device to be increased without reducing thegate length 351 over the active silicon regions (causing an increase inleakage power) and without significantly altering the parasiticcapacitance.

Therefore, disclosed above are planar and non-planar field effecttransistor (FET) structures and methods of forming the structures. Thestructures are made up of segmented active devices (e.g., multipleparallel semiconductor fins for a non-planar transistor or multipleparallel semiconductor layer sections for a planar transistor) connectedat opposite ends to source/drain bridges. A gate electrode is patternedon the segmented active devices between the source/drain bridges suchthat it has a reduced length between the segments (i.e., between thesemiconductor fins or sections). Source/drain contacts land on thesource/drain bridges such that they are opposite only those portions ofthe gate electrode with the reduced gate length. These FET structurescan be configured to simultaneously maximize the density of thetransistor, minimize leakage power and maintain the parasiticcapacitance between the source/drain contacts and the gate conductorbelow a preset level, depending upon the performance and densityrequirements. By decreasing capacitance between the contacts and gatesswitching speed can be improved and switching power can be decreased.Additionally, by increasing the gate length, manufacturing tolerancescan be increased and, hence, device yield can be improved.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and, therefore, such adaptations and modifications should and areintended to be comprehended within the meaning and range of equivalentsof the disclosed embodiments. It is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodiments ofthe invention have been described in terms of preferred embodiments,those skilled in the art will recognize that the embodiments of theinvention can be practiced with modification within the spirit and scopeof the appended claims.

1. A method of forming a planar field effect transistor comprising:forming a semiconductor layer with a plurality of first sections and aplurality of second sections such that said second sections traversesaid first sections and such that said first sections and said secondsections are separated by spaces; patterning a gate conductor on saidsemiconductor layer such that said gate conductor extends across saidfirst sections and said spaces, such that said gate conductor has firstportions above each of said first sections and second portions aboveeach of said spaces, and such that a first length of said first portionsis greater than a second length of said second portions; and forming aplurality of contacts to said second sections such that said contactsare between said first sections and opposite said second portions. 2.The method of claim 1, further comprising before said patterning of saidgate conductor and said forming of said contacts, predetermining saidfirst length, said second length and a pitch between said contacts inorder to simultaneously maximize transistor density, minimize leakagepower and maintain parasitic capacitance below a preset level.
 3. Themethod of claim 1, wherein said gate conductor is formed such that saidfirst length is approximately 1.2 to 2.5 times longer than said secondlength.
 4. The method of claim 1, further comprising doping said secondsections to form source/drain diffusion regions.
 5. A method of forminga non-planar field effect transistor comprising: forming a plurality ofsemiconductor fins and a plurality of semiconductor mesas on aninsulator layer such that said semiconductor mesas traverse saidsemiconductor fins and such that said semiconductor fins and saidsemiconductor mesas are separated by spaces; patterning a gate conductorabove said semiconductor fins such that said gate conductor extendsacross said semiconductor fins and said spaces, such that said gateconductor has first portions above said semiconductor fins and secondportions above said spaces, and such that a first length of said firstportions is greater than a second length of said second portions; andforming a plurality of contacts to said semiconductor mesas such thatsaid contacts are between said semiconductor fins and opposite saidsecond portions.
 6. The method of claim 5, further comprising beforesaid patterning of said gate conductor and said forming of saidcontacts, predetermining said first length, said second length and apitch between said contacts in order to simultaneously maximizetransistor density, minimize leakage power and maintain parasiticcapacitance below a preset level.
 7. The method of claim 5, wherein saidgate conductor is formed such that said first length is approximately1.2 to 2.5 times longer than said second length.
 8. The method of claim5, further comprising doping said second sections to form source/draindiffusion regions.
 9. A method of forming a planar field effecttransistor comprising: forming a semiconductor layer with a plurality offirst sections and a plurality of second sections such that said secondsections traverse said first sections and such that said first sectionsand said second sections are separated by spaces; patterning a gateconductor on said semiconductor layer such that said gate conductorextends across said first sections and said spaces, such that said gateconductor has first portions above each of said first sections andsecond portions above each of said spaces, and such that a first lengthof said first portions is greater than a second length of said secondportions; and forming a plurality of contacts to said second sectionssuch that said contacts are between said first sections and oppositesaid second portions; further comprising before said patterning of saidgate conductor and said forming of said contacts, predetermining saidfirst length, said second length and a pitch between said contacts inorder to simultaneously maximize transistor density, minimize leakagepower and maintain parasitic capacitance below a preset level.
 10. Themethod of claim 9, wherein said gate conductor is formed such that saidfirst length is approximately 1.2 to 2.5 times longer than said secondlength.
 11. The method of claim 10, further comprising doping saidsecond sections to form source/drain diffusion regions.